Glass ceramics with a lithium silicate crystal phase and the use thereof in dental products are known from the state of the art. For example, EP 1 505 041 describes lithium silicate glass ceramics which, in the form of lithium metasilicate glass ceramics, are processed by means of CAD/CAM processes to form the desired dental restorations, wherein a subsequent heat treatment leads to the conversion of the lithium metasilicate (Li2SiO3) phase into lithium disilicate (Li2Si2O5) phase and thus to the formation of high-strength lithium disilicate glass ceramic. Machining of the glass ceramic after the formation of the lithium disilicate phase is, in particular because of the high strength thereof, time-consuming and associated with high tool wear.
Glass ceramics which contain diopside, CaMgSi2O6, as crystal phase are known. Diopside can form as intermediate phase in amphibole glass ceramics (Höland, Beall, “Glass-Ceramic Technology”, Wiley, USA, 2nd Edition, 2012, p. 151), in apatite glass ceramics (ibid., p. 164) or in basalt glass ceramics (ibid., p. 186).
From WO 2009/140632 (Ohio State University) lanthan oxide-doped bioactive glass ceramics which can contain diopside as a crystal phase are known as component of, for example, dental restorations.
From U.S. Pat. No. 4,560,666 (Hoya Corporation) bioactive glass ceramics are known which can contain apatite and diopside and are intended to be used as material for artificial bones or artificial dental roots. WO 2012/172316 (University of Sheffield) discloses ceramic material for dental restorations, which comprises diopside and leucite as crystal phases. EP 1 132 056 (Tokuyama Corporation) describes a process for the preparation of ceramic tooth crowns using a diopside-containing glass ceramic.
U.S. Pat. No. 4,643,982 (Hoya Corporation) describes high-strength anorthite glass ceramics, which can contain apatite or calcium phosphate crystals as well as optionally further crystal phases such as diopside. Due to the presence of several crystal phases, the glass ceramics are characterized by a high opacity. For this reason, they are not suitable for aesthetically demanding dental restorations. Rather they are intended as implant material or material for root pins for which no particular optical properties are necessary.
U.S. Pat. No. 5,066,619 (Hoya Corporation) describes glass ceramics with a mica phase and at least one further crystal phase selected from enstatite, akermanite, diopside, anorthite and richterite, which are said to be suitable for the preparation of tooth crowns. From U.S. Pat. No. 5,246,889 (Hoya Corporation) mica glass ceramics are likewise known which have zirconium oxide as further crystal phase. In some of the glass ceramics described crystal phases of enstatite, akermanite, diopside, anorthite, richterite and forsterite can also occur.
U.S. Pat. Nos. 4,871,384 and 5,232,878 (both Hoya Corporation) describe bioactive apatite glass ceramics which, among other things, can contain diopside as further crystal phase. The glass ceramics are mainly provided as bone replacement material.
U.S. Pat. Nos. 5,356,436 and 5,711,763 (both TDK Corporation) disclose ceramic materials to replace hard body tissues, which materials have wollastonite, diopside or a combination of these crystal phases.
US 2005/0079226 (Pentax Corporation) describes bioactive glass which can be used as a sintering aid for bone replacement materials and, after crystallization, can contain wollastonite and diopside crystal phases.
However, the known materials have a series of disadvantages. In many cases the translucence of these materials cannot be adjusted over a broad range as is desirable for dental materials which can be used for many purposes. Moreover, simple machining of them is often not possible. In addition, their strength often proves not to be sufficient to allow them to be used as restorative dental material.